Compensating means for variable inductances having magnetic cores



y 27, 1952 E. A. VAN YZEREN 2,598,467

COMPENSATING MEANS FOR VARIABLE INDUCTANCES HAVING MAGNETIC CORESOriginal Filed March 17, 1943 IN V EN TOR. ZWOUDADJZMAN WYZZYZZWPatented May 27, 1952 COMPENSATING MEANS FOR VARIABLE IN- DUCTANCESHAVING MAGNETIC 'CORES Ewoud Adriaan van Yzeren, Eindhoven, Netherlands,assignor to Hartford National Bank and Trust Company, Hartford, Conn.,as trustee Continuation of application Serial No. 479,466, March 17,1943. This application December 20, 1950, Serial No. 213,431. In theNetherlands November 9, 1940 Section 1, Public Law 690, August 8, 1946Patent expires November 9, 1960 This application is a continuation ofapplication Serial No. 479,466, filed March 17th, 1943 by Ewoud Adriaanvan Yzeren, now abandoned.

The invention relates to inductance coils whose inductance can beadjusted by means of a core of magnetic material which is slidable inthe field of the coil and in the axial direction thereof, said coilsbeing referred to hereinafter as slidable-core coils.

Such coils may be utilized inter alia in radioreceiving sets wherein,jointly with a fixed capacity, they form a tunable oscillatory circuit.

Just as ganged tuning condensers such as are utilized in a so-calledstraight set, have to comply with the requirement that the capacities ofall sections should have the same course, there arises, if slide-corecoils are utilized in such a receiver, the requirement that the courseof the inductance of the coils as a function of the displacement shouldbe mutually equal.

With slide-core coils suitable for use in receivers according to thesuperheterodyne principle the course of the inductance of the slidecorecoil of the oscillatory circuit must be such that over the whole of thewave-range the frequency of the oscillatory circuit exhibits a constantdifference with respect to the frequency of the preceding circuits.

In the mass production of slidable core coils, it is generallyimpossible to obtain the desired accuracy of adjustment during themanufacture of such coils. I have found that it is more practicable toprovide an adjustable compensating means for the coil so that theinductance of the coil can have a predetermined range of values whichcan be selected after the manufacture of the coil.

In practice it has been found that for slide-core coils destined foroscillatory circuits with the same tuning, such as the oscillatorycircuits of a straight set, or the high-frequency circuits of asuperheterody-ne receiver, it is sufiicient that adjustment of theinitial (or final) inductance is possible independently of one another.

In order to obtain in superheterodyne receivers the desired frequencydifference with the preced-' ing circuits, the slide-core coil may be soconstructed that at the beginning and at the end of the tuning range thefrequency difference acquires the correct value. It has been found,however, that in the middle of the range there occur inadmissibly highdivergences which may amount to from 60 to '70 kilocycles per second.

The invention has for its object to provide means of compensating theabove-mentioned divergence after the manufacture of the coils.

3 Claims. (01. 336-77) According to the invention, in the neighborhoodof one end or of both ends of the coil there is arranged a body ofconductive material which, when the core is completely slid out of thecoil, is loosely coupled with the latter.

The body may be, for example, of annular shape and the distance betweenthis body and the end of the coil should preferably beadjustable.

The invention will be explained more fully with reference to theaccompanying drawing wherein:

Figure 1 illustrates a variable inductance element of the sliding coretype which is provided with adjustable non-magnetic members foradjusting the maximum and minimum values of the inductance;

Figure 2 illustrates a variable inductance element for a superheterodynereceiver which is of the sliding core type and provided with anadjustable non-magnetic member to improve the tracking in the receiver;

Figure 3 shows curves illustrating the improved tracking relationship ina superheterodyne receiver obtainable with the use of inductanceelements according to the invention;

Figure 4 shows padding curves for a superheterodyne receiver.

Referring to Fig. 1 there is shown at 2 a coil having its turns woundaround a cylindrical coil form or body I. In the neighborhood of theright-hand end of the coil is arranged a discshaped body 3 ofconductive, non-magnetic material, for example of copper. The distanceof the disc 3 with respect to the end of the coil is adjustable by meansof a screw 4.

The other end of the coil is surrounded by an annular body 5 likewise ofconductive, non-magnetic material and the distance of this body withrespect to the coil end proper is adjustable, for example, owing to thefact that screw-threads are cut into the ring and on the coil body. Theslidable core of magnetic material is denoted by 6.

In the shown position of the core the inductance of the coil has theminimum value; if the inductance is too high the ring 5 is displaced tothe right; if the inductance is too low the ring has to be displaced tothe left. It is thus possible to adjust the minimum value of theinductance.

The maximum value of the inductance of the coil is obtained by causingthe core to slide completely to the right so that the whole of the coreis within the coil; If this value is not completely exact, subsequentadjustment thereof may take place in a manner similar to that in whichthe minimum inductance is adjusted by displacing the disc 3. Now aslight correction of the position of the ring will in general benecessary anew since the position of the disc 3 may perhaps slightlyinfluence the minimum inductance. Since, however, when the whole of thecore has slid out of the coil, the disc 3 and the ring 5 are eachcoupled with only a small portion of the coil, the requiredextra-correction is only slight so that in this way an adjustment bothof the minimum and of the maximum values of the inductance can easily berealized.

If circumstances allow it, one of the bodies 5 or 3 may be dispensedwith, in which event correction is possible at only one point. It isobvious that for the adjustment of the bodies 3 and 5 otherconstructions are also possible.

With reference to Figs. 2, 3 and 4 it will now be explained in detail inwhat manner a slide-core coil according to the invention can be adjustedfor the case wherein such a coil is utilized in the oscillator circuitof a superheterodyne receiver, in which event the oscillator circuitmust consequently have a constant frequency difference wtih respect tothe preceding circuits of the apparatus.

In Fig. 3, curve a indicates the desired course of the inductance L as afunction of the length I of the core portion which is within the coil.If this coil is joined with a given condenser to form an oscillatorycircuit which is utilized as a frequency-determining oscillatory circuitin the cal oscillator of a superheterodyne apparatus, the frequencydifference of this oscillatory circuit with respect to thehigh-frequency circuits preceding the frequency changer of the apparatusis consequently always constant.

It would be possible to attempt to approximate the course of theinductance according to curve a in Fig. 3 by utilizing the slide-corecoil shown in Fig. 2, which is constituted by a cylindrical coil body Ion which turns 2 are provided and by a slide-core B which may be causedto slide from the left into the coil. By suitably dimensioning the coilit may be ensured that at the beginning and at the end of the tuningrange the inductance has the correct value. It is thus possible torealize a course of the inductance as is indicated by a curve b in Fig.3. This curve shows that in the middle of the tuning range there occursa considerable divergence from the prescribed course determined by curvea. The frequency difference between the oscillator circuit and thepreceding circuit or circuits consequently differs in the middle of thetuning range considerably from the desired value. In Fig. 4 the socalledpadding curve, i. e. the divergence d as a function of the length Z ofthat portion of the core which is within the coil, is represented by thecurve B.

If now, for example, owing to the use of an iron core having a higherpermeability, the maximum inductance is increased, which step does notinfluence, however, the minimum inductance, the inductance has a courseas is shown by the curve 0 in Fig. 3, with which there occurs adivergence d from the prescribed frequency difference according to thecurve C. The curves 0 and C in Figs. 3 and 4 respectively exhibit at thebeginning and in the middle of the range the desired course; at the endof the range, however, the inductance is too high with the result thatthere an appreciable divergence d from the desired constant frequencydifference is still perceptible.

If now a ring 3 of copper is provided in the manner shown in Fig. 2,which ring reduces the maximum inductance of the coil to the valueprescribed by the curve a, we obtain a padding curve D which exhibits inthe whole of the tuning range only slight divergence d.

It will be clear that other shapes of the inductance curve may beobtained with which the measure in which the slopes of the curves aredifferent, may be influenced by the degree of coupling between the ring3 and the coil 2; also the course of the middle portion of the curve maybe influenced by utilizing a ring at each end of the coil.

Furthermore. it is possible, for example, in superheterodyne receivers,to provide each of the slide-core coils of the preceding circuits alsowith adjustable conductive rings in order to adjust exactly the initialand final values of the inductance, so that the desired equality in thecourse is obtained.

What I claim is:

1. An adjustable inductance tuning unit comprising a coil, a core ofmagnetic material movable into and out of said coil in an axialdirection to vary the inductance thereof between maximum and minimumvalues, a conductive non-magnetic member for and spaced beyond each endof said coil in axial alignment therewith for determining the maximumand minimum inductance values, respectively, of said unit, andadjustable means to space each of said conductive non-magnetic memberswith respect to the ends of said coil to adjust said maximum and minimuminductance values of said unit.

2. An adjustable inductance tuning unit comprising a coil, a core ofmagnetic material movable into and out of said coil in an axialdirection to vary the inductance thereof between maximum and minimumvalues, an annular conductive non-magnetic member for and spaced fromeach end of said coil in axial alignment therewith for determining themaximum and minimum inductance values, respectively, of said unit, andadjustable means to space each of said conductive non-magnetic memberswith respect to the ends of said coil to adjust the maximum and minimuminductance values of said unit.

3. An adjustable inductance tuning unit comprising a coil, a core ofmagnetic material movable into and out of said coil in an axialdirection to vary the inductance thereof between maximum and minimumvalues, an annular conductive nonmagnetic member for and spaced fromthat end of said coil into which said core enters and axially alignedtherewith for adjusting the minimum inductance value of said unit, asecond conductive non-magnetic member for and spaced from the end ofsaid coil remote from that end into which said core enters for adjustingthe maximum inductance value of said unit, and adjustable means to spaceeach of said conductive non-magnetic members with respect to the ends ofsaid coil to adjust the maximum and minimum inductance values of saidunit.

EWOUD ADRIAAN VAN YZEREN.

REFERENCES CITED UNITED STATES PATENTS Name Date Wheeler et al Nov. 19,1940 Number

